The present invention relates to a semiconductor memory device.
A semiconductor memory refers to a memory device formed of semiconductor material such as silicon Si, germanium Ge, gallium arsenide GaAs, indium phospide Inp, etc. Semiconductor memory devices are divided into volatile and non-volatile type memory devices.
The volatile memory device requires a power supply to retain the stored data. The volatile memory device includes a static RAM SRAM, a dynamic RAM DRAM, a synchronous DRAM SDRAM and so on. However, the non-volatile memory device retains data stored in the device even in the absence of a power supply. The non-volatile memory device includes a read only memory ROM, a programmable ROM PROM, an electrically programmable ROM EPROM, an electrically erasable and programmable ROM EEPROM, a flash memory, a phase-change RAM PRAM, a magnetic RAM MRAM, a resistive RAM RRAM, a ferroelectric RAM FRAM, etc. Flash memory devices are divided into NOR and NAND type memory devices.
Portions of a memory cell array in the semiconductor memory device may become faulty due to various causes. The memory cell array includes a redundancy memory area for replacing bad areas. For example, bad areas in the memory cell array may be detected in a test process after a manufacturing process of the semiconductor memory device. However, the redundancy memory area increases the area of the semiconductor memory device. Thus, there is a need for a semiconductor memory device with reduced area that still provides the redundancy memory area.